Semiconductor device

ABSTRACT

An object of the present invention is to provide a semiconductor device capable of suppressing loss in a switching element at high temperature without increasing radiation noise of the switching element. A semiconductor device includes an IGBT including a gate to which a gate signal is input, a temperature detection element that detects temperature of the IGBT, and a capacitance adjustment unit that is arranged between the gate of the IGBT and a reference potential terminal and that adjusts a capacitance between the gate and an emitter of the IGBT according to a detection temperature detected by the temperature detection element.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application filed under 35 U.S.C. §111(a) of International Patent Application No. PCT/JP2022/033784, filedon Sep. 8, 2022, the contents of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to semiconductor devices applied to powerconverters and the like.

BACKGROUND ART

Insulated gate bipolar transistors (IGBTs), bipolar transistors, andmetal-oxide-semiconductor field-effect transistors (MOSFETs) are widelyused as switching elements. These switching elements are generally oftenused in the form of power modules incorporating a plurality of pairs ofswitching elements and free wheeling diodes (FWDs) connected inanti-parallel to the switching elements in a single package.Additionally, development of intelligent power modules (IPMs) in whichdriver circuits and protection functions are added to such power modulesis also being actively pursued.

Power modules and IPMs include a gate capacitor connected to a controlsignal input terminal of a switching element (e.g., the gate of anIGBT). The gate capacitor is used to suppress radiation noise generatedduring turn-on by reducing an instantaneous voltage change (recoveryvoltage change rate (dv/dt)) due to reverse recovery of the freewheeling diode when the switching element switches from an OFF state toan ON state (i.e., at turn-on). The gate capacitor is mounted on acontrol circuit section provided on a control substrate (a printedcircuit board). The gate capacitor is added by a user or the like whouses a power module or IPM.

Additionally, in general, power modules and IPMs are equipped with anoverheat protection function that protects IGBTs from overheating. Toprotect each IGBT from overheating, a temperature detection diode isused that is incorporated together with the IGBT in an IGBT chip. IGBTmodules and IPMs use negative temperature characteristics of the diodeto detect whether the IGBT chip is overheating or not. When IGBT modulesor IPMs detect that the IGBT chip is overheating, they stop operation ofthe IGBT.

PTL 1 (for example, JP H10-313570 A) discloses an IGBT driver circuitcapable of easily switching an IGBT between a high dv/dt normal mode anda low dv/dt mode to facilitate suppression of high-frequency leakagecurrent.

SUMMARY OF INVENTION Technical Problem

In general, the larger the IGBT recovery voltage change rate, thegreater the radiation noise associated with operation of the switchingdevice (e.g., IGBT), but the lower the loss generated by the switchingelement (generated loss). On the other hand, the smaller the recoveryvoltage change rate, the lower the radiation noise associated with theoperation of the switching element, but greater the loss generated bythe switching element. In other words, in the switching element, thereis a trade-off relationship between the radiation noise and thegenerated loss.

Furthermore, recovery voltage change rate tends to decrease as thetemperature of a semiconductor chip incorporating switching elementssuch as IGBTs increases. Therefore, the recovery voltage change rate ina switching element is greater at room temperature than at hightemperature. The radiation noise of the switching element is adjusted bya capacitance value of the gate capacitor so as to be smaller than apredetermined value within an operable temperature range of theswitching element. The capacitance value of the gate capacitor isdetermined by a recovery voltage change rate of the switching element atroom temperature. Due to this, when the temperature of a switchingelement such as an IGBT increases, the recovery voltage change ratebecomes smaller than necessary, leading to an increase in loss generatedby the switching element.

It is an object of the present invention to provide a semiconductordevice capable of suppressing loss in a switching element at hightemperature without increasing radiation noise of the switching element.

Solution to Problem

In order to achieve the above object, a semiconductor device includes aswitching element including a control signal input terminal to which aswitching control signal is input, a temperature detection elementconfigured to detect temperature of the switching element to output adetection temperature, and a capacitance adjustment unit arrangedbetween the control signal input terminal and a reference potentialterminal and configured to adjust a capacitance between a gate and anemitter of the switching element according to the detection temperature.

Advantageous Effects of Invention

According to an aspect of the present invention, loss in a switchingelement at high temperature can be suppressed without increasingradiation noise of the switching element.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit block diagram illustrating a schematic configurationof a power converter including a semiconductor device according to eachembodiment of the present invention;

FIG. 2 is a circuit block diagram illustrating a schematic configurationof a semiconductor device according to Embodiment 1 of the presentinvention;

FIG. 3 is a diagram illustrating an example of a relationship between adetection temperature and a detection voltage in a temperature detectionelement included in the semiconductor device according to Embodiment 1of the present invention;

FIGS. 4A and 4B are diagrams illustrating an example of operation of acapacitance adjustment unit included in the semiconductor deviceaccording to Embodiment 1 of the present invention;

FIG. 5 is a diagram illustrating an example of a relationship betweenreturn current and recovery voltage change rate in the semiconductordevice according to Embodiment 1 of the present invention;

FIG. 6 is a diagram illustrating an example of a relationship betweencollector current and switching loss in an IGBT included in thesemiconductor device according to Embodiment 1 of the present invention;

FIG. 7 is a circuit block diagram illustrating a schematic configurationof a semiconductor device according to Embodiment 2 of the presentinvention; and

FIG. 8 is a circuit block diagram illustrating a schematic configurationof a semiconductor device according to Embodiment 3 of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Each embodiment of the present invention exemplifies devices and methodsfor embodying the technological idea of the present invention, and thetechnological idea of the present invention does not specify materials,shapes, structures, arrangements, and the like of components to thosedescribed below. Various modifications can be made to the technologicalidea of the present invention within the technological scope defined bythe appended claims.

Embodiment 1

(Configuration of Power Converter)

A power converter 1 including semiconductor devices 2 a, 2 b, 2 c, 2 d,2 e, and 2 f (hereinafter, the “semiconductor devices 2 a, 2 b, 2 c, 2d, 2 e, and 2 f” may be abbreviated as the “semiconductor devices 2 a to2 f) according to Embodiment 1 of the present invention is describedusing FIG. 1 . The following description uses an inverter circuit as anexample of the power converter 1 including the semiconductor devices 2 ato 2 f according to the present embodiment. However, the semiconductordevices 2 a to 2 f may also be applied to power converters such asconverter circuits and full-bridge circuits.

As illustrated in FIG. 1 , the power converter 1 is connected to athree-phase AC power supply 3. The power converter 1 includes arectifier circuit 4 that full-wave rectifies three-phase AC power inputfrom the three-phase AC power supply 3 and a smoothing capacitor 5 thatsmooths power rectified by the rectifier circuit 4. Althoughillustration of a specific configuration of the rectifier circuit 4 isomitted, the rectifier circuit 4 is configured by connecting six diodesin a full bridge or by connecting six switching elements in a fullbridge.

A positive-side line Lp is connected to a positive output terminal ofthe rectifier circuit 4, and a negative-side line Ln is connected to anegative output terminal thereof. The smoothing capacitor 5 is connectedbetween the positive-side line Lp and the negative-side line Ln.Additionally, the power converter 1 includes an inverter circuit 2 thatconverts a DC voltage applied between the positive-side line Lp and thenegative-side line Ln into a three-phase AC voltage. The invertercircuit 2 includes semiconductor devices 2 a, 2 c, and 2 e eachincluding an insulated gate bipolar transistor (an example of aswitching element) as, for example, a voltage-controlled switchingelement that forms an upper arm section connected to the positive-sideline Lp and semiconductor devices 2 b, 2 d, and 2 f each including aninsulated gate bipolar transistor 21 that forms a lower arm sectionconnected to the negative-side line Ln. Hereinafter, the insulated gatebipolar transistor is abbreviated as “IGBT 21”.

The IGBT 21 included in the semiconductor device 2 a and the IGBT 21included in the semiconductor device 2 b are connected in series betweenthe positive-side line Lp and the negative-side line Ln to form aU-phase output arm 2U. The IGBT 21 included in the semiconductor device2 c and the IGBT 21 included in the semiconductor device 2 d areconnected in series between the positive-side line Lp and thenegative-side line Ln to form a V-phase output arm 2V. The IGBT 21included in the semiconductor device 2 e and the IGBT 21 included in thesemiconductor device 2 f are connected in series between thepositive-side line Lp and the negative-side line Ln to form a W-phaseoutput arm 2W.

A free wheeling diode 22 is connected in anti-parallel to each of theIGBTs 21 included in the semiconductor devices 2 a to 2 f. Details ofthe IGBT 21 and the free wheeling diode 22 are described later.

A connection portion between the IGBT 21 included in the semiconductordevice 2 a and the IGBT 21 included in the semiconductor device 2 b, aconnection portion between the IGBT 21 included in the semiconductordevice 2 c and the IGBT 21 included in the semiconductor device 2 d, anda connection portion between the IGBT 21 included in the semiconductordevice 2 e and the IGBT 21 included in the semiconductor device 2 f,respectively, are connected to a load, for example, a motor 7.

Each of the semiconductor devices 2 a to 2 f includes a gate drivercircuit 10 that individually controls switching operation of the IGBT21. In FIG. 1 , the gate driver circuit 10 is denoted as “GDU”. In eachof the semiconductor devices 2 a to 2 f, output terminals of the gatedriver circuits 10 are connected to gates (an example of a controlsignal input terminal) G of the IGBTs 21, respectively. Additionally,each of the semiconductor devices 2 a to 2 f includes a gate capacitor(an example of a capacitor) 30 connected to the gate driver circuit 10.Details of the gate driver circuit 10 and the gate capacitor 30 aredescribed later.

The inverter circuit 2 includes a three-phase full-bridge circuit inwhich the U-phase output arm 2U, the V-phase output arm 2V, and theW-phase output arm 2W are connected in parallel, the semiconductordevices 2 a and 2 b that control switching operation of the U-phaseoutput arm 2U, the semiconductor devices 2 c and 2 d that controlswitching operation of the V-phase output arm 2V, and the semiconductordevices 2 e and 2 f that control switching operation of the W-phaseoutput arm 2W.

The power converter 1 includes a controller 6 that controls the gatedriver circuit 10 provided in each of the semiconductor devices 2 a to 2f. The controller 6 is configured to individually output, for example, apulse-shaped input signal Vin to each gate drive circuit 10 provided ineach of the semiconductor devices 2 a to 2 f. This allows the controller6 to control the gate driver circuit 10 provided in each of thesemiconductor devices 2 a to 2 f to drive the IGBT 21 provided in eachof the semiconductor devices 2 a to 2 f by, for example, pulse widthmodulation (PWM).

<Semiconductor Device>

Next, the semiconductor devices according to the present embodiment aredescribed with reference to FIG. 1 and using FIGS. 2 to 6 . Thesemiconductor devices 2 a to 2 f provided in the power converter 1 havethe same configuration and operate in the same manner. Therefore, thesemiconductor devices 2 a to 2 f are described hereinafter using thesemiconductor device 2 a as an example.

(Configuration of Semiconductor Device) A schematic configuration of thesemiconductor device 2 a according to the present embodiment isdescribed with reference to FIG. 1 and using FIG. 2 .

As illustrated in FIG. 2 , the semiconductor device 2 a includes theIGBT (an example of a switching element) 21 including a gate (an exampleof a control signal input terminal) G to which a gate signal (an exampleof a switching control signal) is input and a current detection terminalS used to detect at least one of overcurrent or short-circuit current.The semiconductor device 2 a includes a temperature detection element 23that detects temperature of the IGBT 21. The semiconductor device 2 aincludes a capacitance adjustment unit 11 that is arranged between thegate G of the IGBT 21 and a reference potential terminal 41 and thatadjusts a capacitance between the gate G and an emitter E of the IGBT 21according to a detection temperature detected by the temperaturedetection element 23. A gate capacitor (an example of a capacitor) 30 isarranged between the capacitance adjustment unit 11 and the referencepotential terminal 41. The gate capacitor 30 is provided to reducerecovery voltage change rate during switching of the IGBT 21.

The reference potential terminal 41 is connected to an output terminalof the inverter circuit 2 in the semiconductor devices 2 a, 2 c, and 2 eforming the upper arm section of the inverter circuit 2 (see FIG. 1 ),and is connected to a ground terminal (earth terminal) in thesemiconductor devices 2 b, 2 d, and 2 f forming the lower arm section ofthe inverter circuit 2.

The semiconductor device 2 a includes a current detection circuit 13that detect, as a voltage, a detection current output from the currentdetection terminal S. The semiconductor device 2 a includes a gatesignal generation circuit 12 that generates a gate signal to be input tothe gate G. The semiconductor device 2 a includes a temperaturedetection circuit 15 that detects temperature of the IGBT 21 on thebasis of voltage input from the temperature detection element 23. Thesemiconductor device 2 a includes a protection circuit 14 that protectsthe IGBT 21 from abnormal operation on the basis of the voltage inputfrom the current detection circuit 13 and voltage input from thetemperature detection circuit 15.

The semiconductor device 2 a includes a semiconductor substrate (notillustrated), the capacitance adjustment unit 11, the gate signalgeneration circuit 12, the current detection circuit 13, the protectioncircuit 14, and the temperature detection circuit 15 formed on thesemiconductor substrate, and is provided with the gate driver circuit 10that controls the IGBT 21. The gate capacitor 30 is connected to thegate driver circuit 10. The semiconductor device 2 a includes a printedcircuit board (not illustrated) on which the gate driver circuit and thegate capacitor 30 are mounted. The reference potential terminal 41 isformed, for example, on the printed circuit board.

The semiconductor device 2 a includes a semiconductor element 20including the IGBT 21, the free wheeling diode 22 connected inanti-parallel to the IGBT 21, and the temperature detection element 23.A cathode of the free wheeling diode 22 is connected to a collector C ofthe IGBT 21, and an anode of the free wheeling diode 22 is connected tothe emitter E of the IGBT 21. For example, the semiconductor element 20and the printed circuit board are packaged in one module configuration.

The IGBT 21 is a composite element including a main IGBT through which amain current that is a current to be supplied to the motor 7 flows and asense IGBT through which a detection current for detecting the currentflowing through the main IGBT flows. A gate of the main IGBT and a gateof the sense IGBT are connected to form the gate G of the IGBT 21. Acollector of the main IGBT and a collector of the sense IGBT areconnected to form the collector C of the IGBT 21. An emitter of the mainIGBT is the emitter E of the IGBT 21. An emitter of the sense IGBT isthe current detection terminal S of the IGBT 21. The detection currentis much smaller than the main current, and has a current amount of, forexample, approximately 1/10,000 of the main current.

The collector C of the IGBT 21 included in each of the semiconductordevices 2 a, 2 c, and 2 e (see FIG. 1 ) is connected to thepositive-side line Lp (see FIG. 1 ). The emitter E of the IGBT 21included in the semiconductor device 2 a is connected to the collector Cof the IGBT 21 included in the semiconductor device 2 b (see FIG. 1 ).The emitter E of the IGBT 21 included in the semiconductor device 2 c isconnected to the collector C of the IGBT 21 included in thesemiconductor device 2 d (see FIG. 1 ). The emitter E of the IGBT 21included in the semiconductor device 2 e is connected to the collector Cof the IGBT 21 included in the semiconductor device 2 f (see FIG. 1 ).The emitter E of the IGBT 21 included in each of the semiconductordevices 2 b, 2 d, and 2 f is connected to the negative-side line Ln (seeFIG. 1 ).

As illustrated in FIG. 2 , the gate signal generation circuit 12 isconnected to a signal input terminal Ti provided in the semiconductordevice 2 a. The input signal Vin output from the controller 6 is inputto the gate signal generation circuit 12 via the signal input terminalTi. Although a detailed description is omitted, the gate signalgeneration circuit 12 generates a gate signal (e.g., a pulse signal) ata signal level that can control the IGBT 21 to an ON state (conductingstate) or an OFF state (non-conducting state) on the basis of a signallevel of the input signal Vin input from the signal input terminal Ti.

Additionally, an output signal output from the protection circuit 14 isinput to the gate signal generation circuit 12. When an output signalindicating abnormal operation of the IGBT 21 is input from theprotection circuit 14, the gate signal generation circuit 12 generates agate signal at a signal level that can control the IGBT 21 to the OFFstate regardless of the signal level of the input signal Vin, andoutputs to the IGBT 21. Here, the abnormal operation of the IGBT 21means operation in a state where at least one of a current flowingthrough the IGBT 21 or an operation temperature of the IGBT 21 exceedsan absolute maximum rating.

As illustrated in FIG. 2 , an input of the current detection circuit 13is connected to an output of the current detection terminal S of theIGBT 21, and an output of the current detection circuit 13 is connectedto an input of the protection circuit 14. When the detection currentinput from the current detection terminal S of the IGBT 21 is smallerthan an absolute maximum rated current of the IGBT 21, the currentdetection circuit 13 outputs, for example, an output signal at lowsignal level to the protection circuit 14. On the other hand, when thedetection current input from the current detection terminal S of theIGBT 21 is equal to or larger than the absolute maximum rated current ofthe IGBT 21, the current detection circuit 13 outputs, for example, anoutput signal at high signal level to the protection circuit 14. Thecurrent detection circuit 13, for example, compares a detection voltageobtained by converting the detection current input from the currentdetection terminal S of the IGBT 21 into a voltage with a voltage thatis preset and higher than a voltage corresponding to the absolutemaximum rated current of the IGBT 21 (e.g., 1.5 to 2 times the voltage).This allows the current detection circuit 13 to detect whether or notthe current (e.g., collector current) flowing through the IGBT 21exceeds an operable current amount.

As illustrated in FIG. 2 , an input of the temperature detection circuit15 is connected to an output of the temperature detection element 23. Anoutput of the temperature detection circuit 15 is connected to an inputof the protection circuit 14 that is different from that for the outputof the current detection circuit 13. A connection portion between theinput of the temperature detection circuit 15 and the output of thetemperature detection element 23 is connected to an output of a constantcurrent circuit 16 provided in the gate driver circuit 10. The constantcurrent circuit 16 operates at a power supply voltage Vcc applied to apower supply terminal Tvd provided in the semiconductor device 2 a, andoutputs a constant current having a predetermined value to thetemperature detection element 23. The output of the constant currentcircuit 16 is connected not only to the input of the temperaturedetection circuit 15 but also to an inverting input terminal (−) of acomparator 112 (see below for details) provided in a switch circuit 111.An input impedance of the temperature detection circuit 15 and an inputimpedance of the comparator 112 are high impedance. Therefore, theconstant current output from the constant current circuit 16 hardlyflows through the temperature detection circuit 15 and the comparator112, but flows through the temperature detection element 23.

As illustrated in FIG. 2 , the temperature detection element 23 iscomposed of a plurality (three in the present embodiment) of diodesconnected in series. The diodes are made of, for example, silicon. Thetemperature detection element 23 is arranged between the temperaturedetection circuit 15, the constant current circuit 16, and thecomparator 112 and the reference potential terminal 41. The temperaturedetection element 23 is arranged so as to be in a forward direction fromthe constant current circuit 16 side toward the reference potentialterminal 41 side. Therefore, among the plurality of diodes forming thetemperature detection element 23, the diode arranged on the constantcurrent circuit 16 side has an anode connected to the input of thetemperature detection circuit 15, the output of the constant currentcircuit 16, and the input of the comparator 112. Among the plurality ofdiodes forming the temperature detection element 23, the diode arrangedon the reference potential terminal 41 side has a cathode connected tothe reference potential terminal 41.

In general, the forward voltage of a silicon diode is lower at higherambient temperature than at lower ambient temperature. Therefore, whenconstant current is input from the constant current circuit 16 to thetemperature detection element 23, voltage drop in the temperaturedetection element 23 becomes smaller as the temperature of the IGBT 21increases. As a result, the voltage input from the temperature detectionelement 23 to the temperature detection circuit 15 decreases as thetemperature of the IGBT 21 increases. Accordingly, the temperaturedetection circuit 15 can detect whether or not the temperature of theIGBT 21 exceeds the absolute maximum rating by using the voltage that isinput from the temperature detection element 23 and changes according tothe temperature of the IGBT 21.

When the temperature detected by the temperature detection element 23 islower than a value set on the basis of the absolute maximum ratedtemperature of the IGBT 21, the temperature detection circuit 15outputs, for example, an output signal at low signal level to theprotection circuit 14. On the other hand, when the temperature detectedby the temperature detection element 23 is equal to or higher than thevalue set on the basis of the absolute maximum rated temperature of theIGBT 21, the temperature detection circuit 15 outputs, for example, anoutput signal at high signal level to the protection circuit 14. Thetemperature detection circuit 15, for example, compares a value inputfrom the temperature detection element 23 with a value that is presetand set on the basis of the absolute maximum rated temperature of theIGBT 21. This allows the temperature detection circuit 15 to detectwhether or not the temperature of the IGBT 21 is an operabletemperature.

As illustrated in FIG. 2 , the protection circuit 14 includes twooutputs. One output of the protection circuit 14 is connected to aninput of the gate signal generation circuit 12 that is different fromthat for the input signal Vin. The other output of the protectioncircuit 14 is connected to a signal output terminal To provided in thesemiconductor device 2 a.

When an output signal indicating that a current exceeding an operablerange is flowing through the IGBT 21 (hereinafter may be referred to as“current abnormality signal”) is input from the current detectioncircuit 13, the protection circuit 14 outputs a signal indicating theabnormal state of the IGBT 21 to the gate signal generation circuit 12.When the current abnormality signal is input from the current detectioncircuit 13, the gate signal generation circuit 12 outputs a gate signalcapable of turning off the IGBT 21 to the gate G of the IGBT 21 to stopthe operation of the IGBT 21 at the current exceeding the operablerange. Additionally, when the current abnormality signal is input fromthe current detection circuit 13, the protection circuit 14 outputs analarm signal ALM (e.g., a signal at high signal level) to the signaloutput terminal To. This allows the semiconductor device 2 a to outputthe alarm signal ALM indicating that the IGBT 21 is in the abnormalstate to the controller 6 (see FIG. 1 ).

When an output signal indicating that the IGBT 21 is operating at atemperature exceeding an operable temperature (hereafter may be referredto as “temperature abnormality signal”) is input from the temperaturedetection circuit 15, the protection circuit 14 outputs a signalindicating the abnormal state of the IGBT 21 to the gate signalgeneration circuit 12. When the temperature abnormality signal is inputfrom the temperature detection circuit 15, the gate signal generationcircuit 12 outputs a gate signal capable of turning off the IGBT 21 tothe gate G of the IGBT 21 to stop the operation of the IGBT 21 at thetemperature exceeding the operable range. Additionally, when thetemperature abnormality signal is input from the temperature detectioncircuit 15, the protection circuit 14 outputs the alarm signal ALM (e.g.a signal at high signal level) to the signal output terminal To. Thisallows the semiconductor device 2 a to output the alarm signal ALMindicating that the IGBT 21 is in the abnormal state to the controller 6(see FIG. 1 ).

The protection circuit 14 may be configured to output different alarmsignals ALM to the signal output terminal To when a current abnormalitysignal is input from the current detection circuit 13 and when atemperature abnormality signal is input from the temperature detectioncircuit 15. When a current abnormality signal is input from the currentdetection circuit 13, the protection circuit 14 may output, for example,the alarm signal ALM at high signal level to the signal output terminalTo. On the other hand, when a temperature abnormality signal is inputfrom the temperature detection circuit 15, the protection circuit 14 mayoutput, for example, a pulsed alarm signal ALM to the signal outputterminal To. When neither a current abnormality signal nor a temperatureabnormality signal is input (i.e., when the IGBT 21 is in a normaloperation state), the protection circuit 14 outputs, for example, thealarm signal ALM at low signal level to the signal output terminal To.This allows the controller 6 to determine the operation state of theIGBT 21 on the basis of the alarm signal ALM input from thesemiconductor device 2 a.

As illustrated in FIG. 2 , the capacitance adjustment unit 11 includesthe switch circuit 111 that disconnects the connection between the gateG of the IGBT 21 and the gate capacitor 30 when a detection temperaturedetected by the temperature detection element 23 is equal to or higherthan a predetermined comparison temperature and that connects the gate Gof the IGBT 21 and the gate capacitor 30 when the detection temperatureis lower than the comparison temperature. In the present embodiment, thecomparison temperature is set to, for example, a temperature based onthe absolute maximum rated temperature as the operable temperature ofthe IGBT 21 (a temperature equal to or lower than the absolute maximumrated temperature). The capacitance adjustment unit 11 includes thecomparator (an example of a comparator portion) 112 that compares adetection voltage corresponding to the detection temperature input fromthe temperature detection element 23 and detected by the temperaturedetection element 23 with a comparison voltage V1 corresponding to thecomparison temperature. The capacitance adjustment unit 11 includes avoltage generation portion 113 that generates the comparison voltage V1.

The switch circuit 111 includes, for example, a P-type MOS transistor111 a (an example of a disconnection switch) provided so as to be ableto disconnect the connection between the gate G of the IGBT 21 and thegate capacitor 30. The switch circuit 111 includes, for example, anN-type MOS transistor 111 b (an example of a connection switch) providedso as to be able to discharge electric charge of the gate capacitor 30.

The MOS transistor 111 a and the MOS transistor 111 b have acomplementary configuration in which they are connected in seriesbetween the gate G of the IGBT 21 and the reference potential terminal41. Therefore, the switch circuit 111 is a complementary switch circuitcomposed of the MOS transistors 111 a and 111 b. Accordingly, thecapacitance adjustment unit 11 includes the complementary switchcircuit.

A source of the MOS transistor 111 a is connected to the gate G of theIGBT 21. A drain of the MOS transistor 111 a is connected to a drain ofthe MOS transistor 111 b. A source of the MOS transistor 111 b isconnected to the reference potential terminal 41.

A gate of the MOS transistor 111 a and a gate of the MOS transistor 111b are connected. An output terminal of the comparator 112 provided inthe capacitance adjustment unit 11 is connected to the gate of the MOStransistor 111 a and the gate of the MOS transistor 111 b. The gatecapacitor 30 is connected to the drain of the MOS transistor 111 a andthe drain of the MOS transistor 111 b. A connection portion between thegate of the MOS transistor 111 a and the gate of the MOS transistor 111b is an input terminal of the switch circuit 111. Therefore, thecomparator 112 is arranged on an input side of the switch circuit 111. Aconnection portion between the drain of the MOS transistor 111 a and thedrain of the MOS transistor 111 b is an output terminal of the switchcircuit 111. Therefore, the gate capacitor 30 is arranged on an outputside of the switch circuit 111.

One electrode of the gate capacitor 30 is connected to the drain of theMOS transistor 111 a and the drain of the MOS transistor 111 b. Theother electrode of the gate capacitor 30 is connected to the referencepotential terminal 41. Therefore, the gate capacitor 30 is arrangedbetween the output terminal of the switch circuit 111 and the referencepotential terminal 41 with the one electrode connected to the outputterminal of the switch circuit 111.

FIG. 3 is a diagram illustrating an example of a relationship betweendetection temperature and detection voltage in the temperature detectionelement 23. The horizontal axis of a graph illustrated in FIG. 3represents the detection temperature detected by the temperaturedetection element 23. The vertical axis of the graph illustrated in FIG.3 represents the detection voltage corresponding to the detectiontemperature detected by the temperature detection element 23. The “TV”illustrated in FIG. 3 indicates characteristics of the detection voltagewith respect to the detection temperature of the temperature detectionelement 23 (temperature-voltage characteristics).

As described above, the temperature detection element 23 hascharacteristics in which the detection voltage decreases, for example,linearly as the detection temperature increases. Therefore, asillustrated in FIG. 3 , the temperature detection element 23 hastemperature-voltage characteristics TV that decline rightward. In thesemiconductor device 2 a, a comparison temperature Tc is set that isbased on the absolute maximum rated temperature of the IGBT 21 in thetemperature-voltage characteristics TV. Accordingly, when the detectiontemperature detected by the temperature detection element 23 is lowerthan the comparison temperature Tc, the detection voltage is higher thanthe comparison voltage V1. On the other hand, when the detectiontemperature detected by the temperature detection element 23 is equal toor higher than the comparison temperature Tc, the detection voltage isequal to or lower than the comparison voltage V1.

In the present embodiment, the comparison temperature Tc is set on thebasis of the operable maximum temperature (absolute maximum ratedtemperature) of the IGBT 21. Accordingly, when the detection temperaturedetected by the temperature detection element 23 is lower than thecomparison temperature Tc set on the basis of the absolute maximum ratedtemperature of the IGBT 21, the detection voltage is higher than thecomparison voltage V1. On the other hand, when the detection temperaturedetected by the temperature detection element 23 is equal to or higherthan the comparison temperature Tc, the detection voltage is equal to orlower than the comparison voltage V1.

Returning to FIG. 2 , the voltage generation portion 113 is composed of,for example, a DC power supply. A negative side of the voltagegeneration portion 113 is connected to the reference potential terminal41. The comparison voltage V1 is set on the basis of a voltagecorresponding to the absolute maximum rated temperature of the IGBT 21.

As illustrated in FIG. 2 , the comparator 112 is, for example, ahysteresis comparator composed of an operational amplifier and anunillustrated resistance element. The temperature detection element 23is connected to an inverting input terminal (−) of the comparator 112,and a positive side of the voltage generation portion 113 is connectedto a non-inverting input terminal (+) of the comparator 112. The outputterminal of the comparator 112 is connected to the respective gates ofthe MOS transistor 111 a and the MOS transistor 111 b provided in theswitch circuit 111.

When the detection voltage input from the temperature detection element23 and corresponding to the detection temperature is higher than thecomparison voltage V1 generated by the voltage generation portion 113,the comparator 112 outputs, for example, a signal at low signal level tothe switch circuit 111. Additionally, when the detection voltage inputfrom the temperature detection element 23 is equal to or lower than thecomparison voltage V1 (i.e., when the comparison voltage V1 or lower),the comparator 112 outputs, for example, an output signal at high signallevel to the switch circuit 111. Accordingly, when the detectiontemperature detected by the temperature detection element 23 is equal orhigher than the comparison temperature Tc, the comparator 112 outputs ahigh-level output signal. On the other hand, when the detectiontemperature detected by the temperature detection element 23 is lowerthan the comparison temperature Tc, the comparator 112 outputs alow-level output signal.

Since the MOS transistor 111 a is composed of a P-type MOS, it is turnedoff (non-conducting state) when the output signal output by thecomparator 112 is at high level, and is turned on (conducting state)when the output signal is at low level. Therefore, when the detectiontemperature detected by the temperature detection element 23 is equal toor higher than the comparison temperature Tc (when the output signal ofthe comparator 112 is at high level), the MOS transistor 111 adisconnects the connection between the gate G of the IGBT 21 and thegate capacitor 30 (more specifically, an electrical connection thereofwith the one electrode of the gate capacitor 30). On the other hand,when the detection temperature detected by the temperature detectionelement 23 is lower than the comparison temperature Tc (when the outputsignal of the comparator 112 is at low level), the MOS transistor 111 aconnects the gate G of the IGBT 21 and the gate capacitor 30 (morespecifically, electrically connects the gate G and the one electrode ofthe gate capacitor 30).

Since the MOS transistor 111 b is composed of an N-type MOS, it isturned on (conducting state) when the output signal output by thecomparator 112 is at high level, and is turned off (non-conductingstate) when the output signal is at low level. Therefore, when thedetection temperature detected by the temperature detection element 23is equal to or higher than the comparison temperature Tc (when theoutput signal of the comparator 112 is at high level), the MOStransistor 111 b connects the reference potential terminal 41 and thegate capacitor 30 (more specifically, electrically connects thereference potential terminal 41 and the one electrode of the gatecapacitor 30). Additionally, when the detection temperature detected bythe temperature detection element 23 is lower than the comparisontemperature Tc (when the output signal of the comparator 112 is at lowlevel), the MOS transistor 111 b disconnects the reference potentialterminal 41 from the gate capacitor 30 (more specifically, electricallydisconnects the reference potential terminal 41 from the one electrodeof the gate capacitor 30).

Additionally, in other words, when the comparator 112 outputs a signalindicating that the detection voltage corresponding to the detectiontemperature detected by the temperature detection element 23 is equal toor lower than the comparison voltage V1 corresponding to the comparisontemperature Tc, the MOS transistor 111 a disconnects the connectionbetween the gate capacitor 30 and the gate G of the IGBT 21 (morespecifically, the electrical connection between the one electrode of thegate capacitor 30 and the gate G of the IGBT 21), and the MOS transistor111 b connects the gate capacitor 30 to the reference potential terminal41 (more specifically, electrically connects the one electrode of thegate capacitor 30 to the reference potential terminal 41). On the otherhand, when the comparator 112 outputs a signal indicating that thedetection voltage detected by the temperature detection element 23 ishigher than the comparison voltage V1, the MOS transistor 111 a does notdisconnect the connection between the gate capacitor 30 and the gate G(more specifically, the electrical connection between the one electrodeof the gate capacitor 30 and the gate G), and the MOS transistor 111 bdisconnects the gate capacitor 30 from the reference potential terminal41 (more specifically, electrically disconnects the one electrode of thegate capacitor 30 from the reference potential terminal 41).

Accordingly, when the detection temperature detected by the temperaturedetection element 23 is equal to or higher than the comparisontemperature Tc (when the detection voltage corresponding to thedetection temperature is equal to or lower than the comparison voltageV1 corresponding to the comparison temperature Tc), the switch circuit111 serves to switch to a circuit configuration for discharging theelectric charge of the gate capacitor 30. In other words, the switchcircuit 111 connects the gate capacitor 30 to the reference potentialterminal 41 when the detection temperature detected by the temperaturedetection element 23 is equal to or higher than the comparisontemperature Tc. The comparison temperature Tc is set on the basis of,for example, the operable maximum temperature (absolute maximum ratedtemperature) of the IGBT 21, (e.g., set to equal to or lower than theabsolute maximum rated temperature). Additionally, in this case, theswitch circuit 111 disconnects the connection between the gate G of theIGBT 21 and the gate capacitor 30 (more specifically, the electricalconnection between the gate G of the IGBT 21 and the one electrode ofthe gate capacitor 30). In addition, when the detection temperaturedetected by the temperature detection element 23 is lower than thecomparison temperature (when the detection voltage is higher than thecomparison voltage V1), the switch circuit 111 disconnects the gatecapacitor 30 from the reference potential terminal 41 (morespecifically, electrically disconnects the one electrode of the gatecapacitor 30 from the reference potential terminal 41). Furthermore, inthis case, the switch circuit 111 connects the gate G of the IGBT 21 tothe gate capacitor 30 (more specifically, electrically connects the gateG of the IGBT 21 to the one electrode of the gate capacitor 30).

Although details are described later, the semiconductor devices 2 a to 2f control the switch circuit 111 according to the temperature of theIGBT 21, and disconnect the connection between the gate G of the IGBT 21and the gate capacitor 30 when the IGBT 21 is higher than the comparisontemperature Tc, thereby enabling loss in the IGBT 21 at high temperatureto be suppressed without increasing radiation noise of the IGBT 21.

(Operation of Semiconductor Device)

Operation of the semiconductor device 2 a according to the presentembodiment is described with reference to FIGS. 1 to 3 and using FIGS.4A and 4B. FIGS. 4A and 4B are a diagram illustrating operation of thecapacitance adjustment unit 11. In FIGS. 4A and 4B, the MOS transistors111 a and 111 b are illustrated by circuit symbols of switches tofacilitate understanding of the open and closed states. FIG. 4A is acircuit diagram of the capacitance adjustment unit 11 and the like inwhich the MOS transistor 111 a is in an ON state (conducting state) andthe MOS transistor 111 b is in an OFF state (non-conducting state). FIG.4B is a circuit diagram of the capacitance adjustment unit 11 and thelike in which the MOS transistor 111 a is in an OFF state(non-conducting state) and the MOS transistor 111 b is in an ON state(conducting state).

(Normal Operation)

Assume that when there is no overcurrent or short-circuit currentflowing between the collector C and the emitter E (see FIG. 2 ) of theIGBT 21 and the IGBT 21 operates in an operable temperature range(hereinafter may be referred to as “normal state”), the input signal Vinat, for example, high signal level is input from the controller 6 (seeFIG. 1 ). In this case, the gate signal generation circuit 12 (see FIG.1 ) provided in the semiconductor device 2 a is in a non-operationstate, and outputs no gate signal to the gate G of the IGBT 21.Therefore, the IGBT 21 is turned off. As a result, no current flowsbetween the collector C and the emitter E of the IGBT 21, so that nodetection current also flows from the current detection terminal S (seeFIG. 2 ). Additionally, since the temperature of the IGBT 21 remains,for example, at room temperature, the temperature detection element 23detects a temperature lower than the comparison temperature Tc.

When the IGBT 21 is in the normal state and the gate signal generationcircuit 12 outputs no gate signal to the gate G of the IGBT 21, nodetection current is output from the current detection terminal S of theIGBT 21. Therefore, the current detection circuit 13 (see FIG. 2 )outputs an output signal indicating that the IGBT 21 is in the normaloperation state to the gate signal generation circuit 12.

When the temperature of the IGBT 21 is at room temperature, thedetection voltage output from the temperature detection element 23 is avoltage corresponding to a temperature lower than the absolute maximumrated temperature of the IGBT 21. Therefore, the temperature detectioncircuit 15 (see FIG. 2 ) outputs an output signal indicating that theIGBT 21 is in the normal operation state to the gate signal generationcircuit 12.

When the temperature of the IGBT 21 is at room temperature, thedetection voltage output from the temperature detection element 23 is avoltage corresponding to a temperature lower than the comparisontemperature Tc and is higher than the comparison voltage V1. Therefore,the comparator 112 provided in the capacitance adjustment unit 11outputs an output signal at low signal level to the switch circuit 111(see FIG. 2 ). This causes the switch circuit 111 to electricallyconnect the gate G of the IGBT 21 and the one electrode of the gatecapacitor 30 and electrically disconnect the reference potentialterminal 41 from the one electrode of the gate capacitor 30.

When the input signal Vin at low signal level is input from thecontroller 6 in the normal state where no overcurrent or short-circuitcurrent flows between the collector C and the emitter E of the IGBT 21and the IGBT 21 operates in the operable temperature range, the gatesignal generation circuit 12 goes into operation and outputs, forexample, a gate signal at high signal level to the IGBT 21. As a result,the IGBT 21 switches from the OFF state to the ON state, whereby acollector-emitter current flows between the collector C and the emitterE. In addition, a detection current having a predetermined currentamount based on the collector-emitter current flows from the currentdetection terminal S of the IGBT 21 to the current detection circuit 13.

Since it is the normal state where no overcurrent or short-circuitcurrent flows between the collector C and the emitter E of the IGBT 21,the detection current output from the current detection terminal S ofthe IGBT 21 in this case has a current amount based on the currentflowing through the IGBT 21 in the normal state. Therefore, the currentdetection circuit 13 outputs an output signal indicating that the IGBT21 is in the normal operation state to the gate signal generationcircuit 12.

Ambient temperature of the IGBT 21 is almost equal to or higher thanroom temperature since current flows through the IGBT 21. However,during the normal operation of the IGBT 21, the ambient temperature ofthe IGBT 21 does not rise to the absolute maximum rated temperature ofthe IGBT 21. Therefore, the temperature detection element 23 detects atemperature lower than the comparison temperature Tc. As a result, thetemperature detection circuit 15 outputs an output signal indicatingthat the IGBT 21 is in the normal operation state to the gate signalgeneration circuit 12.

When the IGBT 21 is in the normal state, the current detection circuit13 and the temperature detection circuit 15 output an output signalindicating that the IGBT 21 is in the normal state to the gate signalgeneration circuit 12. Therefore, the gate signal generation circuit 12continues to output a gate signal for transitioning the IGBT 21 from theOFF state to the ON state or for maintaining the ON state to the gate Gof the IGBT 21.

The temperature (i.e., the ambient temperature) of the IGBT 21 duringthe normal operation of the IGBT 21 is lower than the absolute maximumrated temperature. Therefore, the detection voltage output from thetemperature detection element 23 is a voltage corresponding to atemperature lower than the comparison temperature Tc and is higher thanthe comparison voltage V1. This causes the comparator 112 provided inthe capacitance adjustment unit 11 to output an output signal at lowsignal level to the switch circuit 111. As a result, as illustrated inFIG. 4A, the MOS transistor 111 a is turned on, and the MOS transistor111 b is turned off. Thus, the switch circuit 111 connects the gate G ofthe IGBT 21 and the gate capacitor 30, and disconnects the referencepotential terminal 41 from the gate capacitor 30.

The gate signal generation circuit 12 outputs a gate current to the gateG when transitioning the IGBT 21 from the OFF state to the ON state. Byconnecting the gate G of the IGBT 21 and the gate capacitor 30, a partof the gate current flows from the gate signal generation circuit 12 tocharge the gate capacitor 30, as indicated by a dashed arrow in FIG. 4A.As a result, the IGBT 21 is maintained at a predetermined potential evenafter transition from the OFF state to the ON state, and thus canmaintain the ON state.

Thus, the semiconductor devices 2 a to 2 f can connect the gate G of theIGBT 21 and the gate capacitor 30 when the temperature of the IGBT 21 islower than the absolute maximum rated temperature and the IGBT 21transitions from an OFF state to an ON state (turned on). This enablesthe semiconductor devices 2 a to 2 f to reduce the recovery voltagechange rate of the IGBT 21 when the IGBT 21 is turned on, therebyenabling suppression of radiation noise radiated by the IGBT 21.

(Operation at High Temperature)

When the IGBT 21 transitions from the OFF state to the ON state (turnedon) at a temperature equal to or higher than the comparison temperatureTc, the temperature detection element 23 detects a temperature equal toor higher than the comparison temperature Tc. Therefore, the temperaturedetection element 23 outputs a detection voltage based on the detectiontemperature to the non-inverting input terminal (+) of the comparator112 provided in the capacitance adjustment unit 11. The detectionvoltage input to the comparator 112 is a voltage lower than thecomparison voltage V1. Therefore, the comparator 112 outputs an outputsignal at high signal level to the switch circuit 111. This turns offthe MOS transistor 111 a and turns on the MOS transistor 111 b, asillustrated in FIG. 4B. As a result, the switch circuit 111 disconnectsthe electrical connection between the gate G of the IGBT 21 and the gatecapacitor 30, and electrically connects the reference potential terminal41 and the gate capacitor 30. When the gate capacitor 30 is charged, theelectric charge charged in the gate capacitor 30 is discharged to thereference potential terminal 41 via the MOS transistor 111 b, asillustrated by a dashed arrow in FIG. 4B.

Thus, the semiconductor devices 2 a to 2 f disconnect the electricalconnection between the gate G of the IGBT 21 and the gate capacitor 30when the temperature of the IGBT 21 is equal to or higher than thecomparison temperature Tc. As a result, although details are describedlater, the semiconductor devices 2 a to 2 f can reduce loss in the IGBT21 when the IGBT 21 is turned on.

<Effects of Semiconductor Device>

Next, effects of the semiconductor devices according to the presentembodiment are described using the semiconductor device 2 a as anexample, with reference to FIGS. 2 to 4A, 4B and using FIGS. 5 and 6 .FIG. 5 is a diagram illustrating a relationship between a return currentflowing through a free wheeling diode connected in anti-parallel to anIGBT and a voltage change rate when the free wheeling diode (FWD)performs reverse recovery operation. For example, when focusing on thesemiconductor device 2 a and the semiconductor device 2 b, a graphillustrated in FIG. 5 is obtained by a measured value of a returncurrent flowing through the free wheeling diode 22 included in thesemiconductor device 2 b when the IGBT 21 included in the semiconductordevice 2 a is turned on and a measured value of its voltage change rate.However, the semiconductor device used to obtain the graph illustratedin FIG. 5 does not include the capacitance adjustment unit 11 includedin the semiconductor devices 2 a to 2 f.

The horizontal axis of the graph illustrated in FIG. represents thereturn current, and the vertical axis of the graph illustrated in FIG. 5represents the recovery voltage change rate. “Cn25” indicated byconnecting white triangles with a dashed line in FIG. 5 indicates thecharacteristics of the recovery voltage change rate with respect to thereturn current when a gate capacitor is not provided and the temperatureof the IGBT is 25° C. “Ce25” indicated by connecting white circles witha solid line in FIG. 5 indicates the characteristics of the recoveryvoltage change rate with respect to the return current when a gatecapacitor is provided and the temperature of the IGBT is 25° C. “Cn125”indicated by connecting hatched triangles with a dashed line in FIG. 5indicates the characteristics of the recovery voltage change rate withrespect to the return current when a gate capacitor is not provided andthe temperature of the IGBT is 125° C. “Ce125” indicated by connectinghatched circles with a solid line in FIG. 5 indicates thecharacteristics of the recovery voltage change rate with respect to thereturn current when a gate capacitor is provided and the temperature ofthe IGBT is 125° C. In the characteristics Ce25 and the characteristicsCe125, the semiconductor devices are provided with a gate capacitorhaving the same capacitance value.

On the horizontal axis of the graph illustrated in FIG. 5 , the returncurrent increases from left to right. On the vertical axis of the graphillustrated in FIG. 5 , the recovery voltage change rate increases frombottom to top. Here, the configuration “not having a gate capacitor”means a configuration in which a gate capacitor is not connected to thegate of the IGBT. Additionally, the configuration “having a gatecapacitor” means a configuration in which a gate capacitor is connectedbetween the gate of the IGBT and the reference potential terminal.

FIG. 6 is a diagram illustrating a relationship between a collectorcurrent flowing through the IGBT at a temperature of 125° C. and aswitching loss in the IGBT. FIG. 6 illustrates a graph obtained frommeasured values of the collector current and switching loss in the IGBT.The horizontal axis of the graph illustrated in FIG. 6 represents thecollector current flowing through the IGBT. The vertical axis of thegraph illustrated in FIG. 6 represents the switching loss in the IGBT.The switching loss in the IGBT illustrated here is a combined loss of aloss during a transition of the IGBT from the OFF state to the ON stateand a loss during reverse recovery of the free wheeling diode (FWD). Thecharacteristics Cn125 have the same content as the characteristics Cn125in FIG. 5 , and the characteristics Ce125 have the same content as thecharacteristics Ce125 in FIG. 5 . On the horizontal axis of the graphillustrated in FIG. 6 , the collector current increases from left toright. On the vertical axis of the graph illustrated in FIG. 6 , theswitching loss increases from bottom to top.

As illustrated in FIG. 5 , a comparison between the characteristics Cn25and the characteristics Cn125 or a comparison between thecharacteristics Ce25 and the characteristics Ce125 shows that therecovery voltage change rate of the IGBT is higher at low IGBTtemperature than at high IGBT temperature. Additionally, a comparisonbetween the characteristics Cn25 and the characteristics Ce25 or acomparison between the characteristics Cn125 and the characteristicsCe125 shows that the recovery voltage change rate of the IGBT is higherwhen the semiconductor device does not include a gate capacitor thanwhen it includes a gate capacitor. Accordingly, the recovery voltagechange rate of the IGBT is maximum when the semiconductor device doesnot include a gate capacitor and the temperature of the IGBT is lowest(25° C. in FIG. 5 ). Radiation noise emitted from the IGBT becomeslarger as the recovery voltage change rate of the IGBT becomes higher.Therefore, the radiation noise emitted from the IGBT is maximum when thesemiconductor device does not include a gate capacitor and thetemperature of the IGBT is lowest (25° C. in FIG. 5 ).

Additionally, the comparison between the characteristics Cn25 and thecharacteristics Ce25 or the comparison between the characteristics Cn125and the characteristics Ce125 shows that the gate capacitor has theeffect of reducing the recovery voltage change rate of the IGBT.Therefore, the gate capacitor has the effect of suppressing radiationnoise of the IGBT. Accordingly, the radiation noise of the IGBT isgreater when the IGBT is at low temperature than when at hightemperature.

As illustrated in FIG. 6 , the switching loss in the IGBT is reduced by3% to 8% without the gate capacitor than with the gate capacitor.Although illustration is omitted, the switching loss in the IGBT isreduced without the gate capacitor than with the gate capacitor even atother temperatures.

Incidentally, the radiation noise of the IGBT can cause malfunction ofother electronic components forming the semiconductor device andequipment arranged around the semiconductor device. Therefore, asemiconductor device including an IGBT requires reduction of radiationnoise of the IGBT within a temperature range where the IGBT can operate.It is thus desirable for the semiconductor device to include a gatecapacitor capable of reducing radiation noise of the IGBT even when theIGBT is at low temperature (25° C. in FIG. 5 ).

However, when a semiconductor device includes a gate capacitor that caneffectively reduce radiation noise generated at low IGBT temperature,loss generally increases compared to when including a gate capacitorthat can effectively reduce radiation noise generated at high IGBTtemperature. Furthermore, regardless of IGBT temperature, IGBT lossgenerally increases when the semiconductor device includes a gatecapacitor than when not including a gate capacitor. Accordingly, asemiconductor device that includes a gate capacitor capable ofeffectively reducing radiation noise generated at low IGBT temperaturecannot effectively reduce noise and loss in the IGBT at high IGBTtemperature.

On the other hand, the semiconductor devices 2 a to 2 f according to thepresent embodiment includes the capacitance adjustment unit 11.Therefore, even when the semiconductor devices 2 a to 2 f include thegate capacitor 30 whose capacitance value is adjusted so as to be ableto effectively reduce radiation noise generated when the IGBT 21 is atlow temperature, the electrical connection between the gate capacitor 30and the gate G of the IGBT 21 can be disconnected when the IGBT 21 is ina high temperature state. This enables the semiconductor devices 2 a to2 f to obtain the effect of reducing radiation noise of the IGBT 21(i.e., the effect of reducing the recovery voltage change rate of theIGBT 21) and also suppress loss generated from the IGBT at hightemperature (generated loss).

As described above, the semiconductor devices 2 a to 2 f according tothe present embodiment includes the IGBT 21 including the gate G towhich a gate signal is input, the temperature detection element 23 thatdetects temperature of the IGBT 21, and the capacitance adjustment unit11 arranged between the gate G of the IGBT 21 and the referencepotential terminal 41 and configured to adjust the capacitance betweenthe gate G and the emitter E of the IGBT 21 according to a detectiontemperature detected by the temperature detection element 23. As aresult, the semiconductor devices 2 a to 2 f can suppress loss in theIGBT 21 at high temperature without increasing radiation noise of theIGBT 21.

Embodiment 2

Semiconductor devices according to Embodiment 2 of the present inventionare described using FIG. 7 . The semiconductor devices according to thepresent embodiment are characterized in that the capacitance between thecontrol signal input terminal of the switching element and the referencepotential terminal can be adjusted stepwise according to the temperatureof the IGBT. A power converter including the semiconductor devicesaccording to the present embodiment is the same as the power converter 1including the semiconductor devices according to Embodiment 1 above, sothat FIG. 1 is referred to as needed below, and a description thereof isomitted. Additionally, in the description of the semiconductor devicesaccording to the present embodiment, components that perform the sameactions and functions as those of the components of the semiconductordevices according to Embodiment 1 above are denoted by the samereference signs, and descriptions thereof are omitted.

The semiconductor devices 2 a to 2 f (see FIG. 1 ) provided in the powerconverter in the present embodiment have the same configuration andoperate in the same manner. Therefore, the semiconductor devices 2 a to2 f are described hereinafter using the semiconductor device 2 a as anexample.

FIG. 7 is a circuit block diagram illustrating a schematic configurationof a semiconductor device 2 a according to the present embodiment. Forease of understanding, FIG. 7 illustrates only voltage generationportions as capacitance adjustment units included in the semiconductordevice 2 a.

As illustrated in FIG. 7 , the semiconductor device 2 a according to thepresent embodiment includes the IGBT (an example of a switching element)21 including the gate (an example of a control signal input terminal) Gto which a gate signal (an example of a switching control signal) isinput and the current detection terminal S used to detect at least oneof overcurrent or short-circuit current. The semiconductor device 2 aincludes the temperature detection element 23 that detects temperatureof the IGBT 21.

The semiconductor device 2 a includes a plurality (three in the presentembodiment) of capacitance adjustment units 11-1, 11-2, and 11-3. Thecapacitance adjustment units 11-1, 11-2, and 11-3 are arranged betweenthe gate G of the IGBT 21 and the reference potential terminal 41 andconfigured to adjust the capacitance between the gate G and the emitterE of the IGBT 21 according to a detection temperature detected by thetemperature detection element 23. The semiconductor device 2 a includesa plurality (three in the present embodiment) of gate capacitors 30-1,30-2, and 30-3 (an example of a capacitor) respectively associated withthe capacitance adjustment units that are any one of the plurality ofcapacitance adjustment units 11-1, 11-2, and 11-3 and that are differentfrom each other. The gate capacitor 30-1 is associated with thecapacitance adjustment unit 11-1. The gate capacitor 30-2 is associatedwith the capacitance adjustment unit 11-2. The gate capacitor 30-3 isassociated with the capacitance adjustment unit 11-3.

The capacitance adjustment units 11-1, 11-2, and 11-3 have the sameconfiguration as that of the capacitance adjustment unit 11 (see FIG. 2) in Embodiment 1 above. The gate capacitor 30-1 is connected to theswitch circuit 111 (see FIG. 2 ) provided in the capacitance adjustmentunit 11-1. The gate capacitor 30-2 is connected to the switch circuit111 provided in the capacitance adjustment unit 11-2. The gate capacitor30-3 is connected to the switch circuit 111 provided in the capacitanceadjustment unit 11-3.

The plurality of capacitance adjustment units 11-1, 11-2, and 11-3control the switch circuit 111 by comparing comparison temperatureshaving different values from each other with a detection temperaturedetected by the temperature detection element 23 (see FIG. 2 ). Asillustrated in FIG. 7 , the voltage generation portion 113 provided inthe capacitance adjustment unit 11-1 is configured to generate acomparison voltage V1, the voltage generation portion 113 provided inthe capacitance adjustment unit 11-2 is configured to generate acomparison voltage V2, and the voltage generation portion 113 providedin the capacitance adjustment unit 11-3 is configured to generate acomparison voltage V3.

The comparison voltage V1 is set to a temperature equal to or lower thanthe absolute maximum rated temperature of the IGBT 21 (hereinafterreferred to as “comparison temperature T1”). The comparison voltage V2is set to a voltage higher than the comparison voltage V1. Therefore,the voltage value of the comparison voltage V1 is set to the samevoltage value as that of a detection voltage output when the temperaturedetection element 23 detects the comparison temperature T1 as thetemperature of the IGBT 21. The voltage value of the comparison voltageV2 is set to the same voltage value as that of a detection voltageoutput when the temperature detection element 23 detects a temperaturelower than the comparison temperature T1 by a predetermined amount(hereinafter referred to as “comparison temperature T2”). The voltagevalue of the comparison voltage V3 is set to the same voltage value asthat of a detection voltage output when the temperature detectionelement 23 detects a temperature lower than the comparison temperatureT2 by a predetermined amount and higher than room temperature by apredetermined amount (hereinafter may be referred to as “comparisontemperature T3”).

Accordingly, the capacitance adjustment unit 11-3 disconnects anelectrical connection between one electrode of the gate capacitor 30-3and the gate G of the IGBT 21 at a detection temperature (comparisontemperature T3) lower than in the capacitance adjustment units 11-1 and11-2, and electrically connects the one electrode of the gate capacitor30-3 and the reference potential terminal 41. The capacitance adjustmentunit 11-2 disconnects an electrical connection between one electrode ofthe gate capacitor 30-2 and the gate G of the IGBT 21 at a detectiontemperature (comparison temperature T2) lower than in the capacitanceadjustment unit 11-1, and electrically connects the one electrode of thegate capacitor 30-2 and the reference potential terminal 41. Similarlyto the capacitance adjustment unit 11 in Embodiment 1 above, thecapacitance adjustment unit 11-1 disconnects an electrical connectionbetween one electrode of the gate capacitor 30-1 and the gate G of theIGBT 21 at a detection temperature (comparison temperature Ti) equal toor lower than the absolute maximum rated temperature of the IGBT 21 by apredetermined amount, and electrically connects the one electrode of thegate capacitor 30-1 and the reference potential terminal 41.

More specifically, when the temperature detection element 23 detects atemperature lower than the comparison temperature T3, the detectionvoltage is higher than the comparison voltages V1 to V3. In this case,the comparator 112 provided in each of the capacitance adjustment units11-1, 11-2, and 11-3 outputs an output signal at low signal level to theswitch circuit 111. Therefore, the MOS transistors 111 a provided in theswitch circuits 111 of each of the capacitance adjustment units 11-1,11-2, and 11-3 are all turned on, and the MOS transistors 111 b providedin the switch circuits 111 are all turned off. This causes the gatecapacitors 30-1, 30-2, and 30-3 to be all electrically connected to thegate G of the IGBT 21 and electrically disconnected from the referencepotential terminal 41. As a result, the gate capacitors 30-1, 30-2, and30-3 are connected in parallel between the gate G of the IGBT 21 and thereference potential terminal 41. Assuming that the capacitance value ofthe gate capacitor is C1, the capacitance value of the gate capacitor isC2, and the capacitance value of the gate capacitor 30-3 is C3, acapacitance value between the gate G of the IGBT 21 and the referencepotential terminal 41 is “C1+C2+C3” (except for a parasitic capacitanceCge between the gate G of the IGBT 21 and the reference potentialterminal 41). When the capacitance value of “C1+C2+C3” is the same asthe capacitance value of the gate capacitor 30 in Embodiment 1 above,the semiconductor devices 2 a to 2 f according to the present embodimentcan achieve the same radiation noise reduction effect and the sameswitching loss reduction effect as those of the semiconductor devices 2a to 2 f according to Embodiment 1 above at room temperature.

When the temperature detection element 23 detects a temperature equal tothe comparison temperature T3 or lower than the comparison temperatureT2 (i.e., a temperature that is higher than room temperature by apredetermined amount), the detection voltage is a voltage within a rangeof from the comparison voltage V3 to higher than the comparison voltageV2. In this case, the comparator 112 provided in the capacitanceadjustment unit 11-3 outputs an output signal at high signal level tothe switch circuit 111. On the other hand, each comparator 112 providedin the capacitance adjustment units 11-1 and 11-2 outputs an outputsignal at low signal level to the switch circuit 111. Therefore, the MOStransistor 111 a provided in the switch circuit 111 of the capacitanceadjustment unit 11-3 is turned off, and the MOS transistor 111 bprovided in the switch circuit 111 is turned on. On the other hand, theMOS transistors 111 a provided in the switch circuits 111 of each of thecapacitance adjustment units 11-1 and 11-2 are both turned on, and theMOS transistors 111 b provided in the switch circuits are both turnedoff.

This causes the one electrode of the gate capacitor to be disconnectedfrom the electrical connection with the gate G of the IGBT 21 andelectrically connected to the reference potential terminal 41. On theother hand, the one electrodes of each of the gate capacitors 30-1 and30-2 are both electrically connected to the gate G of the IGBT 21, andelectrically disconnected from the reference potential terminal 41. As aresult, the gate capacitors 30-1 and 30-2 are connected in parallelbetween the gate G of the IGBT 21 and the reference potential terminal41, and the capacitance value between the gate G of the IGBT 21 and thereference potential terminal 41 is “C1+C2” (except for the parasiticcapacitance Cge between the gate G of the IGBT 21 and the referencepotential terminal 41).

Thus, the semiconductor devices 2 a to 2 f can reduce the capacitancevalue of gate capacitor connected between the gate G of the IGBT 21 andthe reference potential terminal 41 when the comparison temperature T3higher than a normal temperature of the IGBT 21 by a predeterminedamount is detected.

When the temperature detection element 23 detects a temperature equal tothe comparison temperature T2 or lower than the comparison temperatureT1, the detection voltage is a voltage within a range of from thecomparison voltage V2 to higher than the comparison voltage V1. In thiscase, the comparator 112 provided in the capacitance adjustment unit11-2 outputs an output signal at high signal level to the switch circuit111 provided in the capacitance adjustment unit 11-2. Similarly, thecomparator 112 provided in the capacitance adjustment unit 11-3 outputsan output signal at high signal level to the switch circuit 111 providedin the capacitance adjustment unit 11-3. On the other hand, eachcomparator 112 provided in the capacitance adjustment unit 11-1 outputsan output signal at low signal level to the switch circuit 111.Therefore, the MOS transistors 111 a provided in the switch circuits 111of each of the capacitance adjustment units 11-2 and 11-3 are turnedoff, and the MOS transistors 111 b provided in the switch circuits 111thereof are turned on. On the other hand, the MOS transistor 111 aprovided in the switch circuit 111 of the capacitance adjustment unit11-1 is turned on, and the MOS transistor 111 b provided in the switchcircuit 111 is turned off.

This causes the one electrode of each of the gate capacitors 30-2 and30-3 to be disconnected from the electrical connection with the gate Gof the IGBT 21 and electrically connected to the reference potentialterminal 41. On the other hand, the one electrode of the gate capacitor30-1 is electrically connected to the gate G of the IGBT 21, and iselectrically disconnected from the reference potential terminal 41. As aresult, the gate capacitor 30-1 is connected between the gate G of theIGBT 21 and the reference potential terminal 41, and the capacitancevalue between the gate G of the IGBT 21 and the reference potentialterminal 41 is “C1” (except for the parasitic capacitance Cge betweenthe gate G of the IGBT 21 and the reference potential terminal 41).

Thus, when a temperature within the range of from the comparisontemperature T2 to lower than the comparison temperature Ti is detected,the semiconductor devices 2 a to 2 f can reduce the capacitance value ofgate capacitor connected between the gate G of the IGBT 21 and thereference potential terminal 41 compared to when a temperature withinthe range of from the comparison temperature T3 to lower than thecomparison temperature T2 is detected.

When the temperature detection element 23 detects a temperature equal toor higher than the comparison temperature Ti, the detection voltage isequal to or lower than the comparison voltage V1. In this case, thecomparator 12 provided in the capacitance adjustment unit 11-2 outputsan output signal at high signal level to the switch circuit 111 providedin the capacitance adjustment unit 11-2. Similarly, the comparator 12provided in the capacitance adjustment unit 11-3 outputs an outputsignal at high signal level to the switch circuit 111 provided in thecapacitance adjustment unit 11-3. Additionally, the comparator 12provided in the capacitance adjustment unit 11-1 outputs an outputsignal at high signal level to the switch circuit 111. Therefore, theMOS transistors 111 a provided in the switch circuits 111 of each of thecapacitance adjustment units 11-1, 11-2, and 11-3 are turned off, andthe MOS transistors 111 b provided in the switch circuits 111 thereofare turned on.

This causes the one electrode of each of the gate capacitors 30-1, 30-2,and 30-3 to be disconnected from the electrical connection with the gateG of the IGBT 21 and electrically connected to the reference potentialterminal 41. As a result, since none of the gate capacitors 30-1, 30-2,and 30-3 are connected between the gate G of the IGBT 21 and thereference potential terminal 41, the capacitance value between the gateG of the IGBT 21 and the reference potential terminal 41 is “0”. (exceptfor the parasitic capacitance Cge between the gate G of the IGBT 21 andthe reference potential terminal 41).

In this manner, when a temperature equal to or higher than thecomparison temperature T3 is detected, the semiconductor devices 2 a to2 f can reduce the capacitance value of gate capacitor connected betweenthe gate G of the IGBT and the reference potential terminal 41 comparedto when a temperature within the range of from the comparisontemperature T3 to lower than the comparison temperature T1 is detected.

Thus, the semiconductor devices 2 a to 2 f according to the presentembodiment can adjust stepwise the capacitance between the gate G of theIGBT 21 and the reference potential terminal 41 according to a detectiontemperature detected by the temperature detection element 23. As aresult, the semiconductor devices 2 a to 2 f according to the presentembodiment can more effectively reduce radiation noise and switchingloss of the IGBT 21 according to the temperature of the IGBT 21 than thesemiconductor devices 2 a to 2 f according to Embodiment 1 above.

As described above, the semiconductor devices 2 a to 2 f according tothe present embodiment include the plurality of capacitance adjustmentunits 11-1, 11-2, and 11-3 and the plurality of gate capacitors 30-1,30-2, and 30-3 respectively associated with the capacitance adjustmentunits that are any one of the plurality of capacitance adjustment units11-1, 11-2, and 11-3 and that are different from each other. Theplurality of capacitance adjustment units 11-1, 11-2, and 11-3 areconfigured to compare the comparison temperatures Ti, T2, T3 havingmutually different values with a detection temperature detected by thetemperature detection elements 23 to control the switch circuits 111.

This allows the semiconductor devices 2 a to 2 f according to thepresent embodiment to adjust stepwise the capacitance between the gate Gof the IGBT 21 and the reference potential terminal 41 according to thedetection temperature detected by the temperature detection element 23.As a result, the semiconductor devices 2 a to 2 f according to thepresent embodiment can suppress the loss of the IGBT 21 according to thetemperature of the IGBT 21 without increasing the radiation noise of theIGBT 21 in addition to the effects of the semiconductor devices 2 a to 2f according to Embodiment 1 above.

Embodiment 3

Semiconductor devices according to Embodiment 3 of the present inventionare described using FIG. 8 . The semiconductor devices according to thepresent embodiment are characterized in that the capacitance between thecontrol signal input terminal of the switching element and the referencepotential terminal can be continuously adjusted according to thetemperature of the IGBT. A power converter including the semiconductordevices according to the present embodiment is the same as the powerconverter 1 including the semiconductor devices according to Embodiment1 above. Therefore, FIG. 1 is referred to as needed below, and adescription thereof is omitted. Additionally, in the description of thesemiconductor devices according to the present embodiment, componentsthat perform the same actions and functions as those of the componentsof the semiconductor devices according to Embodiment 1 above are denotedby the same reference signs, and descriptions thereof are omitted.

The semiconductor devices 2 a to 2 f (see FIG. 1 ) provided in the powerconverter in the present embodiment have the same configuration andoperate in the same manner. Therefore, the semiconductor devices 2 a to2 f are described hereinafter using the semiconductor device 2 a as anexample.

FIG. 8 is a circuit block diagram illustrating a schematic configurationof a semiconductor device 2 a according to the present embodiment.

As illustrated in FIG. 8 , a gate capacitor 31 included in thesemiconductor device 2 a according to the present embodiment is avariable capacitance capacitor. The gate capacitor 31 has a capacitancevariable depending on a voltage input to a control terminal thereof.

The semiconductor device 2 a according to the present embodimentincludes a non-inverting amplifier circuit 114 in addition to thecapacitance adjustment unit 11 included in the semiconductor device 2 aaccording to Embodiment 1 above. An output of the non-invertingamplifier circuit 114 is connected to the control terminal of the gatecapacitor 31.

More specifically, the non-inverting amplifier circuit 114 includes anamplifier 114 a having a non-inverting input terminal (+) connected tothe output of the temperature detection element 23 and composed of, forexample, an operational amplifier. An output terminal of the amplifier114 a is connected to the control terminal of the gate capacitor 31. Thenon-inverting amplifier circuit 114 includes a resistance element 114 bhaving one terminal connected to an inverting input terminal (−) of theamplifier 114 a and the other terminal connected to the referencepotential terminal 41. The non-inverting amplifier circuit 114 includesa resistance element 114 c connected between the inverting inputterminal (−) of the amplifier 114 a and the output terminal of theamplifier 114 a. The resistance element 114 c has one terminal connectedto the output terminal of the amplifier 114 a and the other terminalconnected to the inverting input terminal (−) of the amplifier 114 a andthe one terminal of the resistance element 114 b. The resistance element114 b and the resistance element 114 c form a feedback circuit.

The non-inverting amplifier circuit 114 is configured to amplify adetection voltage input from the temperature detection element 23 withan amplification factor based on a ratio of a resistance value of theresistance element 114 b and a resistance value of the resistanceelement 114 c and output to the control terminal of the gate capacitor31. The temperature detection element 23 outputs a lower detectionvoltage as the temperature of the IGBT 21 is higher (the detectiontemperature is higher). Therefore, the non-inverting amplifier circuit114 outputs a lower output voltage to the control terminal of the gatecapacitor 31 as the detection temperature detected by the temperaturedetection element 23 is higher. The gate capacitor 31 hascharacteristics in which the lower the voltage input to the controlterminal, the smaller the capacitance value, for example. Accordingly,the semiconductor device 2 a according to the present embodiment canreduce the capacitance value of the gate capacitor 31 as a detectiontemperature detected by the temperature detection element 23 increases.

Additionally, the capacitance adjustment unit 11 in the presentembodiment includes the switch circuit 111. Therefore, the semiconductordevice 2 a can disconnect the connection between the gate capacitor 31and the gate G of the IGBT 21 when the detection temperature detected bythe temperature detection element 23 is equal to or higher than acomparison temperature set on the basis of the absolute maximum ratedtemperature of the IGBT 21.

As described above, the semiconductor devices 2 a to 2 f according tothe present embodiment includes the capacitance adjustment unit 11. Thisenables the semiconductor devices 2 a to 2 f according to the presentembodiment to obtain the same effects as those of the semiconductordevices 2 a to 2 f according to Embodiment 1 above. Additionally, thesemiconductor devices 2 a to 2 f according to the present embodimentincludes the variable capacitance gate capacitor 31. This enables thesemiconductor devices 2 a to 2 f according to the present embodiment toadjust the capacitance between the IGBT 21 and the reference potentialterminal 41 according to a detection temperature detected by thetemperature detection element 23. As a result, the semiconductor devices2 a to 2 f according to the present embodiment can achieve suppressionof the loss of the IGBT 21 according to the temperature of the IGBT 21without increasing the radiation noise of the IGBT 21.

The present invention is not limited to the above embodiments, and canbe modified in various ways.

Although the semiconductor devices 2 a to 2 f according to the aboveembodiments include the IGBT 21 as the switching element, the presentinvention is not limited thereto. The switching element included in thesemiconductor devices may be an IGBT, a bipolar transistor, or a MOStransistor. In addition, the switching element may be a wide bandgapsemiconductor element including SiC, GaN, diamond, gallium nitride-basedmaterial, gallium oxide-based material, AlN, AlGaN, ZnO, or the like.

Although the MOS transistor 111 a and the MOS transistor 111 b in theabove embodiments have the complementary configuration in which they areconnected in series between the gate G of the IGBT 21 and the referencepotential terminal 41, the present invention is not limited thereto. Theswitches provided in the capacitance adjustment units 11, 11-1, 11-2,and 11-3 need not have a complementary configuration as long as theyoperate in the same manner as complementary switch circuits. Forexample, a plurality of (e.g., two) switches (e.g., MOS transistors)provided in the capacitance adjustment units 11, 11-1, 11-2, and 11-3may be configured to be individually controlled by different signals.

The technological scope of the present invention is not limited to theexemplary embodiments depicted and described, but rather encompasses allembodiments that provide advantageous effects equivalent to thoseintended by the present invention. Additionally, the technological scopeof the present invention is not limited to combinations of features ofthe present invention defined by the claims, but rather can also bedefined by any other desired combination of specific features of alldisclosed individual features.

REFERENCE SIGNS LIST

-   -   1: Power converter    -   2: Inverter circuit    -   2 a, 2 b, 2 c, 2 d, 2 e, 2 f: Semiconductor device    -   2U: U-phase output arm    -   2V: V-phase output arm    -   2W: W-phase output arm    -   3: Three-phase AC power supply    -   4: Rectifier circuit    -   5: Smoothing capacitor    -   6: Controller    -   7: Motor    -   10: Gate driver circuit    -   11, 11-1, 11-2, 11-3: Capacitance adjustment unit    -   12: Gate signal generation circuit    -   13: Current detection circuit    -   14: Protection circuit    -   15: Temperature detection circuit    -   16: Constant current circuit    -   20: Semiconductor element    -   21: IGBT    -   22: Free wheeling diode    -   23: Temperature detection element    -   30-1, 30-2, 30-3, 31: Gate capacitor    -   41: Reference potential terminal    -   111: Switch circuit    -   111 a, 111 b: MOS transistor    -   112: Comparator    -   113: Voltage generation portion    -   114: Non-inverting amplifier circuit    -   114 a: Amplifier    -   114 b, 114 c: Resistance element    -   ALM: Alarm signal    -   C: Collector    -   E: Emitter    -   G: Gate    -   Ln: Negative-side line    -   Lp: Positive-side line    -   S: Current detection terminal    -   T1, T2, T3, Tc: Comparison temperature    -   Ti: Signal input terminal    -   To: Signal output terminal    -   Tvd: Power supply terminal    -   V1, V2, V3: Comparison voltage    -   Vcc: Power supply voltage    -   Vin: Input signal

1. A semiconductor device comprising: a switching element including acontrol signal input terminal where a switching control signal is input;a temperature detection element configured to detect temperature of theswitching element to output a detection temperature; and a capacitanceadjustment unit arranged between the control signal input terminal and areference potential terminal and configured to adjust a capacitancebetween a gate and an emitter of the switching element according to thedetection temperature.
 2. The semiconductor device according to claim 1,wherein a capacitor is arranged between the capacitance adjustment unitand the reference potential terminal.
 3. The semiconductor deviceaccording to claim 2, wherein the capacitance adjustment unit includes aswitch circuit configured to disconnect a connection between the controlsignal input terminal and the capacitor when the detection temperatureis equal to or higher than a predetermined comparison temperature, andconnects the control signal input terminal and the capacitor when thedetection temperature is lower than the comparison temperature.
 4. Thesemiconductor device according to claim 3, wherein the switch circuitserves to switch to a circuit configuration for discharging electriccharge of the capacitor when the detection temperature is equal to orhigher than the comparison temperature.
 5. The semiconductor deviceaccording to claim 3, wherein the switch circuit includes adisconnection switch provided to be able to disconnect the connectionbetween the control signal input terminal and the capacitor.
 6. Thesemiconductor device according to claim 5, wherein the disconnectionswitch disconnects the connection between the control signal inputterminal and the capacitor when the detection temperature is equal to orhigher than the comparison temperature, and connects the control signalinput terminal to the capacitor when the detection temperature is lowerthan the comparison temperature.
 7. The semiconductor device accordingto claim 5, wherein the switch circuit includes a connection switchprovided to able to discharge the electric charge of the capacitor. 8.The semiconductor device according to claim 7, wherein the connectionswitch connects the reference potential terminal to the capacitor whenthe detection temperature is equal to or higher than the comparisontemperature, and disconnects the reference potential terminal from thecapacitor when the detection temperature is lower than the comparisontemperature.
 9. The semiconductor device according to claim 7, whereinthe disconnection switch and the connection switch include acomplementary configuration in which the switches are connected inseries between the control signal input terminal and the referencepotential terminal.
 10. The semiconductor device according to claim 7,wherein the capacitance adjustment unit includes a comparator portionconfigured to compare a detection voltage input from the temperaturedetection element and corresponding to the detection temperature with acomparison voltage corresponding to the comparison temperature, in whichwhen the comparator portion outputs a signal indicating that thedetection voltage is equal to or lower than the comparison voltage, thedisconnection switch disconnects the connection between the capacitorand the control signal input terminal, and the connection switchconnects the capacitor to the reference potential terminal, and when thecomparator portion outputs a signal indicating that the detectionvoltage is higher than the comparison voltage, the disconnection switchdoes not disconnect the connection between the capacitor and the controlsignal input terminal, and the connection switch disconnects thecapacitor from the reference potential terminal.
 11. The semiconductordevice according to claim 3, comprising: a plurality of the capacitanceadjustment units; and a plurality of the capacitors respectivelyassociated with the capacitance adjustment units that are any one of theplurality of capacitance adjustment units and that are different fromeach other, wherein the plurality of capacitance adjustment unitscompares the comparison temperatures including mutually different valueswith the detection temperature to control the switch circuit.
 12. Thesemiconductor device according to claim 2, wherein the capacitor is avariable capacitance capacitor.